The Alpha-fetoprotein (AFP) and albumin genes of the mouse provide a powerful model system for investigating the mechanisms by which organisms generate diversity in the patterns of gene expression. These genes are found tightly linked on mouse chromosome 5, and arose from 300 to 500 million years ago-as the result of a gene duplication. Their expression is co-activated in at least four separate cell lineages in the mouse; the visceral endoderm of the yolk sac, the fetal liver, gut and kidney. Yet within these tissues they exhibit very different rates of transcription, which, in the case of the AFP gene, change dramatically in liver after birth. This application wishes to address four issues. First, the DNA sequence elements responsible for the activation of these genes in the four lineages will be identified by gene transfer techniques into both tissue culture cells and mice. The sequences responsible for the postnatal suppression of the AFP gene will be identified by using the ability of AFP genes in transgenic mice to undergo selective repression. Second the tran-acting protein factors which recognize these elements will be identified and cloned using both biochemical and genetic selection methods. Third using teratocarcinoma cells as a model system, the role that cell-cell interaction plays in the decision of the primary endoderm to form either visceral or parietal endoderm will be investigated. In these studies we will focus on the role of the basement membrane in eliciting the secondary induction of the AFP gene during the maturation of the visceral endoderm, and will use anti-sense RNA strategies to interfere with the orderly development of the extra-cellular matrix. Fourth, the gene or genes responsible for that decision will be cloned using phenotypic selection schemes following gene transfer.